1. Field of the Invention
The present invention relates to the formation of capacitors, resistors, printed circuit boards, microelectronic devices, and the like. In particular, it relates to a process for manufacturing a multilayered construction for use in preparing thin film resistor-conductor materials and the like.
2. Description of the Related Art
As the circuitry design of central processing units (CPU) seeks to achieve increased operational speed, the performance of integrated circuits becomes ever more important. The circuitry design of printed circuit boards, which mount these integrated circuits, is also very important.
Capacitors and resistors are common elements on printed circuit boards and other microelectronic devices. Capacitors are used to steady the operational power supply of such devices. A capacitor is a device used for introducing capacitance into a circuit, and functions primarily to store electrical energy, block the flow of direct current, or permit the flow of alternating current. They comprise a dielectric material sandwiched between two electrically conductive metal layers, such as copper foils. In general, the dielectric material is coupled to the electrically conductive metal layers via an adhesive layer, by lamination, or by vapor deposition.
Heretofore, capacitors arranged on the surface of printed circuit boards have been common. However, more recently, capacitors are formed of a thin, double-sided copper clad laminate within multilayered circuit board layers thus producing excellent characteristics. Of these options, it has been preferred to form printed circuit boards having embedded capacitors to maximize the surface area of the circuit board for other purposes. In order to achieve increased signal transmission speed, printed circuit board manufacturers generally form printed circuit boards within such a multilayer structure. The capacitance of a capacitor depends primarily on the shape and size of the capacitor layers and the dielectric constant of the insulating material. There are various known types of dielectric materials known in the art. For example, the dielectric material may be a gas, such as air, a vacuum, a liquid, a solid or a combination thereof. Each material has its own particular properties.
The performance of conventional capacitors for use in printed circuit boards has been limited by factors such as limited minimum thickness of their dielectric material, which detracts from the flexibility of the capacitor, the attainable capacitance, the effect of bond enhancers on the metal foils, low dielectric constant, and poor dielectric strength.
It is desirable to form a capacitor for circuit boards having a high dielectric constant and an extremely thin layer of dielectric material, thus increasing the capacitance and flexibility of the capacitor. To optimize the performance of a capacitor, it is important that the dielectric material employed have good material properties, exhibiting such qualities as superior adhesion, high dielectric strength and good flexibility. However, common problems frequently associated with extremely thin dielectric layers are the formation of microscopic voids or other structural defects and inclusion of foreign material.
These lead to electrical shorts. For example, U.S. Pat. Nos. 5,155,655 and 5,161,086 describe a method for forming a capacitor wherein a single sheet of a dielectric material is laminated together with two conductive foils. Dielectric layers of this type are highly vulnerable to the formation of voids, as well as the inclusion of foreign material, and are time consuming to detect and remedy.
U.S. Pat. No. 6,693,793 relates to a structure having a pair of conductive foils, a pair of thin dielectric layers, with one dielectric layer on a surface of each of the foils. The two conductive foils are adhered together such that the dielectric layers are attached to one another via an intermediate heat resistant film layer. This capacitor offer a significant improvement in performance over prior art capacitors and printed circuit boards. The thin dielectric layers allow for higher capacitance, greater heat conductivity and greater flexibility of the capacitor. The intermediate heat resistant film layer deters the formation of electrical shorts between the electrically conductive foils.
Conventional methods for manufacturing circuit elements include the attaching components of the structure in sequential order of the layers. However, several disadvantages result in the sequential attaching of certain layers of a structure. For example, some materials cannot be attached or formed onto other materials with desired precision and uniformity. In addition, some materials fail to provide enough strength to support other materials which must be formed thereon, or attached thereto. Furthermore, manufacturing costs associated with some materials and processes, such as electroplating, make it undesirable to attach certain layers in a sequential order.
It would be desirable to provide a method of forming a multilayered construction which has both capacitive and resistive elements, and which method also overcomes the problems associated with conventional processing steps. The present invention provides a method for forming such a multilayered structure for resistor and capacitor formation. The structure formed by this method provides high capacitance, greater heat conductivity, and greater flexibility, while also incorporating a resistor element. The inventive method also results in better precision and uniformity of such a structure and its component layers during assembly. This method further maximizes cost effectiveness in the manufacturing of such multilayered constructions.